Vehicles are often loaned to a friend or family member. Usually this involves physical hand-off of a key, or placement of the key in a secure or secret location until the borrower arrives at a vehicle. Of course, this means that the owner will have to arrange some manner of physical key transfer and return.
Ride-sharing systems for loaning a vehicle to the general public or renting a vehicle may use a digital key provided to a renter or borrower. The borrower/renter can use this key (or code) to unlock and start the vehicle. Typically, the borrower will utilize an application or website through a third party to obtain the key and pay for vehicle usage. Again, this involves some level of advance planning by the owner, although that planning may be limited to an initial sign up and ensuring the vehicle is left in an accessible location for the renter.